This invention generally relates to electric lamps and has particular reference to an improved incandescent lamp having filament-lead wire junctures that facilitate lamp manufacture and enhance product quality.
The standard practice in the incandescent lamp industry with regard to electrically connecting the tungsten filament coil to the lead-in wires is to either clamp the inner ends of the lead wires around the ends of the filament or provide the filament coil with leg portions that are welded to the leads. Clamped connections are rather costly and time consuming and are also somewhat critical since they require careful control of the clamping operation to prevent crushing or breaking the filament while, at the same time, avoiding loose clamps and unreliable junctures. Welding of the filaments to the lead wires is accordingly more prevalent but it also entails production and quality problems, particularly in the manufacture of compact halogen-cycle incandescent lamps which have molybdenum inner lead wires and thus require tungsten-to-molybdenum welds to fasten the end portions of the filament to the respective leads. In order to reduce the incidence of poor welds, a suitable flux such as platinum (either in the form of a foil or a coating on the molybdenum leads) must be used when making such welds. This, of course, further complicates lamp manufacture and increases the cost.
A filament connection for an electric incandescent lamp wherein the leg portions of a coiled tungsten filament are welded to one or more transverse ridge portions that are provided on each of the ends of nickel lead wires which are also flattened and specially configured is disclosed in U.S. Pat. No. 2,227,324 granted Dec. 31, 1940 to Severin. A similar filament connection which also employs specially-flattened lead wire ends and includes a groove or V-recess in the tips of the lead wires to provide additional support for the filament legs is disclosed in U.S. Pat. No. 2,632,126 issued Mar. 17, 1953 to Curtis.
The use of lead wires having flattened ends or which are constructed from two different kinds of metal to facilitate electrical connection with the ends of the filament are disclosed in U.S. Pat. Nos. 324,038 to Moses and U.S. Pat. No. 508,659 to Thomson. An incandescent lamp wherein the ends of the tungsten filament are embedded in the fused ends of the lead wires which are melted with the aid of a flux is disclosed in U.S. Pat. No. 1,022,554 to Howell. A method of making a welded juncture for the cathode of an electron tube by using tabs of platinum and tantalum which serve as flux materials and permit a tungsten filament to be welded to a tungsten lead is disclosed in U.S. Pat. No. 2,341,716 issued Feb. 15, 1944 to Herdman.